The invention relates to a cyclic internal combustion engine with an independent and constant-volume combustion chamber.
Cyclic internal combustion engines with an independent combustion chamber and separate compression and expansion chamber as described in French Patents 2319769 or alternatively 2416344 allow a certain number of improvements to be made to the operation compared with conventional engines. In this type of engine, inlet and compression take place in a chamber controlled by a piston, whereas expansion and exhaust take place in another chamber; the independent combustion chamber is connected to these chambers by ducts equipped with shutters. However, the variable volumes of these two chambers are controlled cyclically in phase and the time available for the combustion and transfer of the gaseous masses is particularly short and does not allow complete combustion to be achieved as is achieved in conventional engines.
The engine according to the invention makes it possible to alleviate this shortcoming and to make a considerable improvement in the operation of this type of engine; it is characterized by the means employed, and more specifically by the fact that the compression chamber cycle, which comprises inlet and compression, is advanced in relation to the expansion chamber cycle which comprises expansion and exhaust so that it is possible to obtain a combustion time which is far longer than in conventional engines; as a tangible example, in a conventional engine and in the engines described in the aforementioned patents, the combustion of their charge takes place over approximately 30 to 45xc2x0 of rotation of their engine shaft, whereas with the engine procedure according to the invention there are up to 180xc2x0 of rotation available (during the exhaust stroke) in which to fill the chamber and burn the mixture, and this, depending on the mode of filling used, may allow combustion periods of the order of 150xc2x0 or even 160xc2x0 of rotation of the engine shaft. Furthermore, and in order to avoid heat loss through the walls during this lengthy combustion, the chamber will or may be coated with a thermal barrier made of ceramic or other heat-insulating materials so as not to lose heat through the walls which can thus be very hot; likewise it will be particularly advantageous, this also for the same reasons, for the walls of the expansion chamber (piston crown, roof of the chamber, transfer duct, etc.) to be coated with a thermal barrier made of ceramic or other heat-insulating materials.
The operation of the engine according to the invention and the improvements made over conventional engines and over the engines described in the aforementioned patents will now be understood. The interdependency, in particular, in terms of compression chamber and expansion chamber cycle, and the thermal protection of the combustion chamber and/or of the expansion chamber allow combustion periods 3 to 4 times longer than those of conventional engines to be achieved without significant heat loss, and thus allow the efficiency to be improved; incidentally, it is also possible with this arrangement to be able to produce a combustion chamber which does not depend, at its base, on the diameter of the piston, and thus to approximate to or to achieve the ideal spherical shape without roughnesses or xe2x80x9ccornersxe2x80x9d in which the gases do not burn and produce unburnt hydrocarbons.
These combined advantages of a long combustion period, of a compact combustion chamber shape close to that of a sphere without roughnesses or corners, thermally insulated with hot walls make it possible to obtain emissions of pollutants in the exhaust which are far lower than in conventional engines.
According to another embodiment of the invention, it is possible to form between the compression chamber and the combustion chamber a buffer volume in which compressed air is accumulated which will make it possible to avoid surge effects and pressure drops due to the dead transfer volumes and to the expansion during the filling of the combustion chamber.
The mode of operation of the compressor can therefore vary without this in any way altering the principle of the invention; although in common practice it seems convenient to employ a reciprocating compressor, any other mode of producing compressed air may be usedxe2x80x94a single or multi-stage reciprocating compressor, a rotary vane compressor, a Roots-type blower or Lyshom type compressor or a turbocompressor driven by the exhaust gases. Likewise, for certain applications it is possible to employ a reserve of air from a cylinder (or other container) which will be expanded in the combustion chamber, or even compressed air from a main (in the example of a stationary engine used in a factory employing compressed air from a main).
The mode of operation of the expansion chamber can also vary without this in any way altering the principle of the invention; although in practice it also seems convenient to employ a piston sliding in a cylinder and driving a crankshaft via a connecting rod, any rotary encapsulation system can also be usedxe2x80x94rotary with radial vanes, with rotary piston such as the path of a conchoid of a circle or of a trochoid, etc.
The engine according to the invention operates with homogeneous air-fuel mixtures and the mixing can be achieved using a carburetor prior to inlet into the compressor, but it is preferable to have a fuel-injection (electronic or mechanical) system between the compressor and the combustion chamber, although direct injection into the combustion chamber can also be used without that in any way altering the operating principle.
The engine according to the invention also operates with heterogeneous self-igniting mixtures like in diesel engines. In this case, the spark plug fitted into the chamber is omitted and a direct diesel injector supplied by a pump and its equipment of a type commonly used in diesel engines is fitted into the said combustion chamber.
Incidentally, there may be inserted at least two separate combustion chambers operating in exactly the same way as the one described hereinabove and which can be supplied together, separately or alternately in order to improve the thermodynamic efficiency at light loadxe2x80x94for example using just one chamber for used power levels below half the total power of the engine, and using both chambers above that value.